ActiveRecord協會：我做對了嗎？

Question

我正在構建一個簡單的Rails應用程序（這是我的第一個rails項目），用於跟蹤組內用戶的統計信息。我使用遷移腳本創建了表格，當我在MySql中查看時，一切看起來都很好，但是當我將它們連接到另一個表格時，並非所有模型都會返回數據。

有人發現我的模型，遷移腳本或數據模型有什麼問題嗎？

這裏是我的移民文件的腳本代碼：

class CreateGroupsUsers < ActiveRecord::Migration 
    def change 

    create_table :types do |t| 
     t.string :name 
    end 

    create_table :groups do |t| 
     t.string :name 
     t.belongs_to :type, index: true 
    end 

    create_table :users do |t| 
     t.string :username 
     t.string :email 
     t.string :first_name 
     t.string :last_name 
     t.string :e_password 
     t.string :salt 
     t.timestamps 
    end 

    create_table :roles do |t| 
     t.string :name 
    end 

    create_table :groups_users, id: false do |t| 
     t.belongs_to :group, index: true 
     t.belongs_to :user, index: true 
     t.belongs_to :role, index: true 
    end 

    create_table :statistics do |t| 
     t.string :name 
    end 

    create_table :groups_users_statistics, id: false do |t| 
     t.string :value 
     t.belongs_to :group, index: true 
     t.belongs_to :user, index: true 
     t.belongs_to :statistic, index: true 
    end 

    end 
end 

這裏是我的我的模型：

class Type < ActiveRecord::Base 
    has_many :groups 
end 

class Role < ActiveRecord::Base 
    has_many :groups_users 
end 

class User < ActiveRecord::Base 
    has_and_belongs_to_many :groups 
    has_one :roles, through: :groups_users 
end 

class Group < ActiveRecord::Base 
    has_and_belongs_to_many :users 
    has_one :types 
end 

class Statistic < ActiveRecord::Base 
    //i'm not too sure how to define this model 
end 

，這裏是我的數據模型

Answer 1

我更新我的模型根據Esse，Pavan和AndyV的評論。一切似乎是工作的罰款，現在

class Type < ActiveRecord::Base 
    has_many :groups 
end 

class Role < ActiveRecord::Base 
    has_many :group_users 
end 

class User < ActiveRecord::Base 
    has_many :group_users 
    has_many :groups, through: :group_users 

    has_many :group_user_statistics 
    has_many :groups, through: :group_user_statistics 
    has_many :statistics, through: :group_user_statistics 
end 

class Group < ActiveRecord::Base 
    has_many :group_users 
    has_many :users, through: :group_users 

    has_many :group_user_statistics 
    has_many :users, through: :group_user_statistics 
    has_many :statistics, through: :group_user_statistics 
end 

class GroupUser < ActiveRecord::Base 
    belongs_to :group 
    belongs_to :user 
end 

class Statistic < ActiveRecord::Base 
    has_many :group_user_statistics 
    has_many :groups, through: :group_user_statistics 
    has_many :users, through: :group_user_statistics 
end 

class GroupUserStatistic < ActiveRecord::Base 
    belongs_to :user 
    belongs_to :group 
    belongs_to :statistic 
end